feat(ui): show file path and Reset to Scanned in the metadata editor

Complete the metadata editor modal to match the backend override work:

- File Path: read-only, monospace field showing the resolved on-disk
  location (MediaDetail.FileLocation), next to Format and File Size, so
  admins can see exactly which file backs the record without leaving the
  editor. Renders empty for non-admins, who never receive the path.
- Reset to Scanned: new button beside Rescan. It confirms, then calls
  POST /api/media-items/:id/rescan?reset_overrides=true to drop all
  per-field user overrides and re-extract scanned defaults. Rescan alone
  keeps customizations; Reset discards them.

web/src/book-detail.ts

@@ -96,6 +96,7 @@ interface MetadataEditorState {
   coverAction: string;
   saving: boolean;
   rescanning: boolean;
+  resetting: boolean;
   userRating: number;
   ratingHover: number;
   ratingSaving: boolean;
@@ -109,6 +110,7 @@ interface MetadataEditorState {
   removeCover(): void;
   saveMetadata(): Promise<void>;
   rescanBook(): Promise<void>;
+  resetMetadata(): Promise<void>;
   starFill(i: number): string;
   ratingText(): string;
   setRating(value: number): Promise<void>;
@@ -142,6 +144,7 @@ Alpine.data("bookDetail", () => {
     coverAction: "keep",
     saving: false,
     rescanning: false,
+    resetting: false,
     userRating: 0,
     ratingHover: 0,
     ratingSaving: false,
@@ -550,6 +553,41 @@ Alpine.data("bookDetail", () => {
       }
     },
 
+    async resetMetadata() {
+      if (this.resetting) return;
+      if (
+        !window.confirm(
+          "Reset all metadata to scanned defaults? Manual edits and custom covers will be discarded.",
+        )
+      ) {
+        return;
+      }
+      this.resetting = true;
+      const mediaId = getMediaId();
+      try {
+        const resp = await fetch(
+          `/api/media-items/${mediaId}/rescan?reset_overrides=true`,
+          {
+            method: "POST",
+            headers: { Authorization: getAuthHeader() },
+          },
+        );
+        if (!resp.ok) {
+          const err = await resp.json().catch(() => ({}));
+          throw new Error(err.error || "Failed to reset metadata");
+        }
+        showToast("Metadata reset to scanned defaults", "success");
+        setTimeout(() => window.location.reload(), 500);
+      } catch (e) {
+        showToast(
+          e instanceof Error ? e.message : "Failed to reset metadata",
+          "error",
+        );
+      } finally {
+        this.resetting = false;
+      }
+    },
+
     async searchEditorTags() {
       const libraryId = document.body.getAttribute("data-library-id") || "";
       if (!this.tagSearch || this.tagSearch.length < 2 || !libraryId) {